demonstrates the use of the s command, which takes this form: s/replace stuff matching this pattern/with this/. In this case the "with this" is blank, which means it will just remove stuff matching the pattern. \s is an abbreviation for white space characters - space, tab, line feed. + means match one or more such characters in a row. $ means match only if the pattern is found at the very end of a string.

This is an inadequate explanation; see the Tutorials section, especially here.